Vehicle dynamics and personal exposure to black carbon in the vicinity of at-grade pedestrian infrastructure

• Main Author: Williams, David
• Other Authors: North, Robin; Ochieng, Washington
• Published: Imperial College London 2014
• Subjects: 624
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.656730

Urban areas are often subject to traffic-induced poor air quality. Variability in vehicle operating behaviours at traffic management infrastructure leads to increased emission rates of pollutant species harmful to health. Where these locations are also sites of pedestrian activity, exposure to pollution is increased. This thesis demonstrates this mechanism through measurement of vehicle dynamics and emissions modelling, with tailpipe emissions found to be at least 20% greater when the vehicle is delayed due to mid-link crossings. As it has no non-combustion sources, black carbon (BC) is a useful proxy for traffic related emissions. Previous research into air quality at traffic management infrastructure has been of an insufficient scale to identify the variability in pollutant concentration and exposure. This thesis addresses this gap through an investigation into BC concentration and exposure at traffic management infrastructure, demonstrating that fixed monitors over coarse temporal and spatial scales are inadequate for assessing BC concentration and exposure, and finding that public health and transport professionals are ill-equipped to make recommendations for improvements on the basis of current data and understanding. To provide data suitable for an assessment at the micro-scale, a measurement framework is specified for the use of micro-aethalometers in urban areas. This addresses problems of signal noise, aerosol loading and consistency where other studies have not, enabling measurement of BC concentration at higher temporal resolution (5-second) than previously. Micro-aethalometers are deployed at signalised intersections in London and Glasgow (UK). The variability in BC is identified, with median concentration up to 130% greater at pedestrian waiting locations across the intersection. In high traffic flow environments, the periodicity of peak concentration episodes is found to relate to traffic control cycles. High-resolution data are applied to pedestrian exposure studies, with in-transit exposure to BC varying by more than ten times as a result of activity patterns.